Occurrence of a. thyreoidea ima is comparatively rare, though it has been from time to time reported by the investigators. In the course of dissection practice in the year 1954 in our laboratory we found 2 cases of a. thyreoidea ima out of 13 corpses dissected (15.3%). In the one case from the 49-year-old male corpse, the artery originated from a. carotis communis, and in another case from the 68-year-old male corpse the artery originated from truncus brachiocephalicus. It was believed that the former is by far rare than is the latter. In the first case the artery arose from inside of a. carortis communis on the right side proceeding in the right front of trachea up-and inwardly, then slightly turning, it went upwards, reaching finally the lower margin of right lobe of thyroid gland in which it distributed. In the second case the artery arose from upper side of truncus brachiocephalicus, and proceeding in- and upward, then bending out- and upward, it approximated to the lower margin of right lobe of thyroid gland and ramified into two branches, inner and ourer. The inner branch further proceeded upward, while the outer branch proceeded out- and upward as a continuation of the main stem. As they reached the lower margin of the glaod, they increased ramification to de distributed in the gland. It has been claimed by some investigators that the occurrence of this artery is sometimes accompanied by the absence of a. thyreoidea caudalis. The latter, however, was present in both cases. The a. thyreoidea ima is said to be the remnant of a branch of a. thymica abnormally developed after the embryonic stage of life.
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